The invention pertains to supervisable communications systems. More particularly, the invention pertains to such systems which can be used to detect alarm conditions and which incorporate a plurality of programmed processors.
Alarm indicating systems are known and have been recognized as being useful in providing early indications of the presence of abnormal conditions such as smoke or gas. Known systems can be implemented in the form of multi-processor communication systems wherein some of the processors are coupled to ambient condition sensors.
Known systems provide bi-directional communication links, which can be coupled to a control element or control panel, to provide electrical energy and signals to the processors coupled thereto. It has been recognized that the physical length of such links can impose limitations on the number of processors that can be coupled thereto. This can also be affected by the quality of the links.
In addition to wanting to incorporate larger numbers of processors into such systems, there is usually a requirement that the links be supervised in some way. One known form of supervision of electrical cables involves applying test electrical signals, for example a current, to the cables. In the event of an open circuit, the current will cease.
There continues to be a need to be able to support additional numbers of processors on a given communication system for a given level of communication link quality. Additionally, there is a continuing need to be able to supervise the condition of such links so as to be able to deal with communication failures due to, for example, open circuit conditions in wired systems.
A supervisable communication system incorporates at least two communication links, either one of which is capable of supplying electrical energy to a plurality of remote units coupled thereto. Members of a plurality of branches are coupled across the links. Operating units, for example programmed processors, can be coupled to each of the branches.
The operating units can receive electrical energy and communications via the links and the branches. In one aspect, a control element can be coupled to the communication links. In another aspect, the links can be implemented as wire or optical cables.
The control element implements a supervision function of the branches. Communication failures or open circuit conditions can be detected.
At least one isolator is located in each of the branches. The isolators, in response to messages received from the control element can block communications on a respective branch as by open circuiting the branch in a wired system.
By blocking communications on each of the branches, except a selected branch, the selected branch can be evaluated for a non-communication, such as an open circuit, condition. In another aspect, each of the branches can be serially evaluated to determine whether the respective branch exhibits a communication condition or a non-communication condition as, for example, evidenced by an open circuit.
The control element can couple an electrical signal to one of the links. If all but one of the branches has been blocked, for example by open circuiting them, the receipt of that signal on the other link is an indication that the branch being evaluated is exhibiting a communicating state. In the absence of a communicating state, perhaps due to an open circuit in the branch, the electrical signal will not be received at the sensing link.
In a wired communication system wherein the links are implemented with conductive cable and the branches are in turn implemented by conductive cable, an open circuit condition on any of the branches can be identified by the control element. In addition, the location of the open circuit condition on a selected branch can be established, relative to electrical units coupled to the branch.
In yet another aspect, the control element can be implemented using a programmed processor. Sequences of instructions stored at the control element carry out a process of open circuiting all of the branches but one and evaluating a communications parameter of the one branch. In this fashion, each of the branches can be evaluated. Where one or more branches is determined to be exhibiting a non-communication or an open circuited condition, executable instructions at the control element, by transmission of selected signals to the branch can in turn establish the location of the open circuited condition.
Alternate architectures include coupling each of the branches to a multiplexer. The multiplexer, for supervision purposes, can sequence through and select each of the branches for evaluation. In yet another alternate, the ends of each of the branches can be coupled to a common control element. The other end of each branch can be coupled to a communications link or user which in turn is coupled to the control element.